This invention relates generally to solar power systems. More particularly, the present invention relates to solar power systems having a tracking system for accurately pointing a solar collector at the sun throughout the day.
Early solar power systems included solar tracking systems employing two independent drives to tilt the solar collector about two axes. The first, an elevation axis, allowed the collector to be tilted within an angular range of about ninety degrees between “looking at the horizon” and “looking straight up”. The second, an azimuth axis, is required to allow the collector to track from east to west. The required range of angular rotation depends on the earth's latitude at which the solar collector is installed. For example, in the tropics the angular rotation needs more than 360 degrees.
These early solar power tracking systems generally used electric drives having high ratio gear reducers to turn the collector in the direction of the sun. Error in the gear reducers or linkage between the motor and collector, such as backlash and non-linearly, detracted from the accuracy. When high accuracy was required, the gear reducers were very expensive.
These conventional solar power systems occasionally suffered damage from high winds. Thus, it is known to place the solar collector in a wind stow position and avoid damage when winds exceed the design specifications. “Wind stow” is an attitude of the collector that presents the smallest “sail” area to the wind. Generally, a wind sensor was used trigger a command for the elevation actuator to point the collector straight up. The electric elevation actuators and high ratio speed reducers utilized by these systems were very slow to put the collector into wind stow, sometimes taking as long as forty-five minutes. If movement to the wind stow position was initiated at a low threshold value of the wind, to account for the long lead time, the efficiency of the solar power station was adversely affected. If efficiency was optimized by increasing the threshold value of wind required to initiate movement to the wind stow position, a rapidly increasing wind would cause damage to the solar collector.
U.S. Pat. No. 6,123,067 proposed a solar power system that had an exoskeleton structure secured to the rear surface of the solar collection device and that is pivotally secured about a horizontal axis to the front end of an azimuth platform assembly. A hydraulic elevation actuator is pivotally mounted in the azimuth platform assembly about a horizontal axis and the front end of its piston rod is pivotally connected to the rear surface of the solar collection device, allowing the solar collection device to be pivoted approximately 90 degrees between a vertical operating position and a horizontal storage position. Primary and a secondary azimuth hydraulic actuator are used to rotate the collection device for tracking the sun. It was believed that such a tracking system would require less time to move the solar collector to the wind stow position. However, the solar collector of such a solar power system can not be scaled up significantly.